save project

binary_search.py

 # 使用二分查找法，找出9和20在列表里面的索引
 num_list = [1, 3, 5, 8, 11, 15, 17, 18 , 20, 21]
-low = 0
-high = len(num_list)-1
-num = 20
-while low <= high:
-    mid = (low + high)//2
-    guess = num_list[mid]
-    if guess == num:
-        print("找到了，它的索引是:",mid)
-        break
-    elif guess < num:
-        low = mid + 1
-    else:
-        high = num - 1
+def binary_search(alist,num):
+    low = 0            #最低索引
+    high = len(alist)-1#最高索引
+    while low <= high:          #当最低索引小于等于最高索引
+        mid = (low + high)//2
+        guess = num_list[mid]
+        if guess == num:
+            return mid
+        elif guess < num:
+            low = mid + 1
+        else:
+            high = num - 1
+    return None
+r = binary_search(num_list,9)
+print(r)